In a typical factory-powered distribution system, power is generated by a power generation company and supplied to a factory and thereafter distributed around the factory to various equipment such as, for example, motors, welding machinery, computers, heaters, lighting, and the like.
Power distribution systems of this type are typically centrally located in switchgear rooms or substations. From there, power is divided up into branches wherein each branch supplies power to a portion of the factory and/or specified loads. Frequently, there are disposed around the factory transformers to step down the supply voltage to that required by specific pieces of equipment or portions of the factory. Therefore, a factory-powered distribution system typically has a number of transformers servicing various types of equipment in various areas. Inherent with this, is the high cost of the power-distribution equipment such as transformers, as well as the cost of the equipment to which power is being supplied. Therefore, it is quite common to provide protective devices such as circuit breakers or fuses in at least each branch so that not only may each piece of equipment be protected but any problems associated with one piece of equipment does not ripple to adjacent or interconnected pieces of equipment. Further, providing fuses or circuit breakers in each branch can help minimize downtime since specific loads may be energized or de-energized without affecting other loads thereby creating increased efficiencies, lower operating and manufacturing costs and the like.
Typically, when circuit breakers are utilized, they are used to detect more than just large overcurrent conditions caused by short circuit faults. In addition, they frequently detect lower level long-time overcurrent conditions and excessive ground currents. The simplest form of circuit breakers are thermally tripped as a result of heating caused by overcurrent conditions and, in this regard, are basically mechanical in nature. These mechanical-type breakers are incorporated into almost all circuit breakers, regardless of whether or not additional advanced circuitry is provided since they are extremely reliable over a long life cycle, while providing a "default" trip-type level of protection.
These types of thermally tripped mechanical breakers are best used for detecting relatively low-level overcurrent conditions since they reflect the cumulative heating effect of low-level overcurrent conditions over a period of time. However, they do not respond well to high-current short-circuit conditions because the response time is frequently too slow to provide effective protection against such conditions. This is particularly so with modern equipment, such as computers and the like, or computer-operated equipment which are much more sensitive to overcurrent conditions.
Further, it is frequently the case that loads such as motors are now much more closely sized to their particular application in order to obtain maximum energy and cost efficiencies. Therefore, overcurrent conditions are more likely to adversely affect the load, such as the motor. This is a departure from older systems where loads such as motors were frequently oversized, since energy was cheap and oversized motors provided a level of inherent resiliency and protection to overcurrent conditions.
Other types breakers have additional features to monitor the level of current being passed through the branch circuits and trip the breaker when the current exceeds a pre-defined maximum value. This allows a breaker to be adjusted so as to fit a particular load or condition by the end user without designing or specifying different breakers. Breakers of this type typically include a microcontroller coupled to one or more current sensors. The microcontroller continuously monitors the digitized current values using a curve which defines permissible time frames in which both low-level and high-level overcurrent conditions may exist. If an overcurrent condition is maintained for longer than its permissible time frame, the breaker is tripped.
Microcontroller controlled breakers may also include the ability to calculate RMS current values. This is necessary in order to prevent erroneously tripping a circuit breaker when a non-linear load, such as a welding machine, is coupled to the branch that it is protecting. The reason for this is that non-linear loads tend to produce harmonics in the current waveform. These harmonics tend to distort the current waveform, causing it to exhibit peak values which are augmented at the harmonic frequencies. When the microcontroller, which assumes that the current waveform is a sinusoidal current waveform, detects these peaks it may, therefore trip the breaker even though the heating effect of the distorted waveform may not require that the circuit be broken.
Further, microcontrollers in some circuit breakers are used to monitor and control or account for other types of faults, such as over or under voltage conditions and phase loss or imbalances. Such microcontrollers operate solenoids which are operatively connected to the trip mechanism of the circuit breaker. Therefore, while the thermal overload portion of the breaker will operate the trip mechanism, the solenoid will operate at the instruction of the microcontroller (or sometimes also at the instruction of external signals) to allow the trip mechanism to trip the associated circuit breaker.
Further, as a result of the flexibility and breadth of protection that microcontrollers can provide when used in conjunction with circuit breakers, their use in circuit breakers is becoming more and more prevalent to the point of being standard. However, this presents another problem in that microcontrollers and the associated circuitry require power. Such power may be typically provided in one of three ways or a combination thereof and would utilize either batteries, externally-supplied power or power provided by potential transformers. However, users frequently do not like to utilize a separate power supply for each breaker or trip unit since this requires separate or additional wiring. Further, while batteries are generally reliable, they still require charging circuits, maintenance, separate compartments, additional costs and, of course, replacement. Therefore, most users provide one power supply, having battery back-up, for supplying all of the controllers for the entire substation or switchgear closet.
However, even this solution is problematic when the power supply (sometimes referred to as the control voltage) fails or begins to fail, thereby allowing what is known as an under-voltage condition to exist. Such under-voltage conditions may result from temporary overloading, power supply faults or the like. However, regardless of the reason for under-voltage conditions, during such times the microprocessor generally does not have sufficient power to operate properly. Further, electrical standards or customer design requirements dictate that the breaker must be tripped (the circuit opened) when the microcontroller does not have sufficient power to operate such as during such low voltage conditions. Additionally, low voltage conditions may not be able to provide sufficient power to the solenoid, which must be in an energized condition during normal operating conditions in order to allow the breaker to remain closed and hence energized. However, should the under-voltage condition be merely momentary, then equipment will be needlessly de-energized, resulting in downtime, increased costs and perhaps a dangerous condition (e.g. ventilation fans not providing sufficient fresh air).
Further, in order to effect such tripping, heretofore known circuit breakers typically incorporate a solenoid which when energized permits the breaker to be in the closed and energized position. When the solenoid is de-energized, the solenoid armature thereby moves and causes mechanical linkages to operate an associated mechanism on the circuit breaker such that a charged circuit breaker will open. Therefore, heretofore known circuit breakers experiencing under-voltage conditions will cause the solenoid to lose power thereby resulting in nuisance trips or a microcontroller will interrupt power to the solenoid thereby also resulting in opening of a closed/energized circuit breaker.
As previously mentioned, certain electrical standards dictate under what conditions an under-voltage trip device will act to open a charged and closed breaker with the result that typically, when the power supply control voltage drops to 30% or less, a trip coil will be de-energized and similarly, the solenoid not be allowed to reset and seal in, unless and until the rated voltage reaches at least 85% of the rated voltage, with the solenoid prohibiting the breaker from being energized until certain voltage levels are met.
Heretofore, under-voltage trip devices typically used a simple mechanical mechanism whereby the armature of a solenoid trip coil is mated with a spring in order to provide the appropriate settings for drop-out and pick-up points as well as the force required to energize a trip arm in the breaker. However, these devices, as may be guessed, are extremely difficult to set with any degree of accuracy and perhaps, more importantly, lack consistency. Additionally, different power supply voltages typically required a coil with a matching voltage reading. Further, should the trip coil be blocked from picking up for any reason at all, the trip coil may be permanently damaged. Additionally, user selection of drop-out and pick-up points or time delays was unavailable and typically had to be done at the factory under test conditions in order to ensure proper rating.
Further, each breaker type typically required a different device to provide under voltage-tripping functions, even though each breaker-type device may have had the same or similar associated problems. Moreover, such trip devices typically required a great deal of assembly and a variety of stocked parts.
Also, attempts at utilizing RC circuitry in order to hold in a trip coil during momentary dips were difficult to calibrate, bulky and expensive to utilize and required a great variety of configurations depending on the different coils for different type breakers.
Further, great variations in power supply control voltages exists amongst differing users such that trip devices must be reconfigured for each range of power supply control voltages. Such required range of voltages typically vary from 12 VDC to 200 VDC, or 10 VAC to 140 VAC. Therefore, some attempts have been made to provide a trip device power supply which utilizes at least a portion of the above recited power supply control voltages. Such power supplies have attempted to use linear-type regulators to provide the required power supply voltage (typically 5 and/or 12 VDC) although significant amounts of heat are required to be dissipated, thereby limiting the use and type of packages or simply requiring that they be placed in different parts of the breaker or the enclosure in which the breaker is housed. Some trip device power supplies have attempted to use switching regulators, although these have been found to be expensive, complex, require a significant amount of board space and further create a problem in that they require a power source to operate the switching regulators control circuit just to operate the switcher until the switcher can run on its own power, as is the case during start-up or under-voltage conditions. Complicating the fact is that the switcher power-up circuit must operate on the same voltage as the under-voltage trip device.
Therefore, trip device power supplies and power supply control voltage schemes have dictated a significant amount of trade-offs and overall have simply not provided the characteristics necessary or desired without incurring significant cost.